Globus pallidus externus (GPe) is a nucleus in the indirect pathway of basal ganglia circuitry which was originally considered to be a group of homogenous GABAergic projection neurons producing downstream inhibition of subthalamic nuclei (STN). However, recent evidence using genetic reporter lines have revealed that there are three classes of neurons in this region which have different electrophysiology properties and different projections. These cell types include parvalbumin neurons, arkypallidal neurons and Lhx6 neurons. This knowledge has important implications for our basic understanding of GPe physiology and to the GPe dysfunction observed in movement disorders including Parkinson's disease and Huntington's disease. However, there remains a critical gap in our knowledge of glutamatergic system in GPe which can potentially be used to modulate dysfunctional basal ganglia circuitry. In particular the function of various NMDA receptor subtypes in the different classes of GPe neurons is unknown. We propose to address the expression and function of GluN2C/GluN2D subunits in GPe since these receptors have many unusual properties including lower sensitivity to Mg2+-block, higher glutamate/glycine affinity and lack of desensitization which are optimal for tonic activity observed in GPe neurons. Our preliminary data and previous reports suggest that GluN2C/GluN2D may express in a cell-specific manner in GPe. Therefore, activation of GluN2C/GluN2D receptors may produce unique changes in GPe function and downstream inhibition which may allow fine tuning of disrupted basal ganglia circuitry in movement disorders. We will address the functional expression of the GluN2C and/or GluN2D subunits in GPe in a cell-type specific manner and elucidate their roles in cellular excitability and inhibitory tone in STN and potential relevance to behavioral deficits and cortical oscillation abnormalities in Parkinson's disease. We will use a multidisciplinary approach involving electrophysiological and behavioral studies together with pharmacological and DREADD tools as well as genetic and reporter lines and parkinsonian mouse models to address our goals.